In the field of aviation, distance measuring equipment (DME) refers to equipment onboard the aircraft that communicates with a DME ground transponder to determine the distance from the aircraft to the DME ground transponder when the aircraft is within the DME ground transponder's service volume. The DME ground transponder continually transmits a signal, generally referred to as a squitter, which an aircraft receives as it enters the DME station's service volume. When the aircraft wants to receive range data from the DME ground station, the DME onboard the aircraft responds to the squitter by interrogating the DME ground station. Typical applications for DME include navigation while en route, during terminal operations and during the approach and landing phases of a flight. The ground station responds to the interrogation automatically with a known time delay. The DME onboard the aircraft measures the time difference between the original interrogation and the reply and uses this to compute the distance of the aircraft from the DME ground station.
In a conventional arrangement, the DME system onboard the aircraft is a relatively high power (e.g., 1,000 Watts) system with an omni-directional antenna system configured to communicate with the ground station at any bearing (azimuth angle) that may exist between the aircraft and the ground station. Although directional antennas can be used to reduce transmit power requirements, conventional DME systems are provided with a relatively high power, omni-directional antenna system from the original equipment manufacturer (OEM). Replacing the existing omni-directional antenna with a directional antenna and replacing the original DME amplifier with a lower power amplifier is typically not a cost effective option.
In order to reduce size, weight, power and cost it is desirable to integrate the various radios on an aircraft. This is only possible with a multi-function antenna. This interrogation avoids the unnecessary duplication of antennas, RF feeder cables, RF amplifiers and other circuits. The proposed invention aids in the integration of TCAS, DME and the Airborne Transponder functions.